First sketch of a new geological map of Scotland with explanatory notes

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FIRST SKETCH

NEW GEOLOGICAL MAP OF SCOTLAND

EXPLANATORY NOTES

SIB RODERICK I. MURCHISON, D.C.L., F.R.S.

DIRECTOR-GENERAL
AND

ARCHIBALD GEIKIE, F.E.S.E., F.G.S.

GEOLOGIST

OF THE GEOLOGICAL SURVEY OF GREAT BRITAIN

CONSTRUCTED BY A. KEITH JOHNSTON, GEOGRAPHER TO THE QUEEN

EDINBURGH

W. & A. K JOHNSTON, AND W. BLACKWOOD & SONS

E. STANFORD, CHARING CROSS, LONDON

MDCCCLXII.

EARTH

EXPLANATION OF THE MAP AND SECTIONS.

IN laying before the public this Geological Sketch-Map as the
basis of a new classification of the rocks of Scotland, I may
say, on the part of my colleague and myself, that one of our
leading objects is to carry out to their ultimate application the
principles first promulgated by our illustrious countryman
Hutton. The founder of that school of Physical Geology,
which has prevailed, clearly explained the natural causes
through which water-formed sediments, having been derived
from the abrasion of pre-existing continents, had, under
pressure, passed into stone, and further shewed how such
stony masses had often been subsequently metamorphosed into
crystalline stratified rocks, like those of the Scottish Highlands.
The latter view was to a great extent confirmed by the experi-
ments of Hall, and the researches of other followers of Hutton ;
whilst these principles, so admirably illustrated by Playfair
have since been philosophically extended by Lyell.

Still, such a classification of the various rock-formations as
might lead to their delineation in a Geological Map of Scotland,
has necessarily been a slowly progressive work.

Notwithstanding the long-continued lectures and descriptions
of Jameson, and the numerous writings of Macculloch, no
effort was made to embody the details furnished by these
authors in a general map, until a distinguished foreign geolo-
gist, Dr Boue, acquiring knowledge from those teachers, and
making journeys into various districts of Scotland, published
his Essai Geologique sur I'Ecosse, and prefixed to it a minute

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sketch-map, representing rudely the large groups in^0 which
the rocks were then considered to be divisible.

Turning my own attention to the structure of Scotland as
early as 1826, I began to construct for my information a geo-
logical map, which in the subsequent year I completed very
roughly, by colouring the old topographical map of General
Eoy ; but, besides descriptions of the lias and oolitic forma-
tions of Brora, in Sutherland, and the Hebrides, with map and
sections,1 the only general result was a small Geological Map
of the North of Scotland, to illustrate a memoir by Professor
Sedgwick and myself.2

In this brief explanation it is, of coursei impossible to do
justice to the many expositors of Scottish Geology to whose
labours much of the information given on our map is due In
addition to the names of Hutton, Hall, Playfair, Webb Seymour,
Jameson, Boue, and Macculloch, it would ill become us not to
mention with respect those of Hay Cunningham,3 Charles
Maclaren,4 and David Milne (now Mr Milne Home).5 Besides
these we may note, with others, Anderson,6 Bald,7 Craig,8
Duff,9 Fleming,10 Edward Forbes,11 James D. Forbes,12 Hark-
ness,13 Hibbert,14 Imrie,15 Landale,16 Lord Greenock,17 Mac-

1 Trans. Geol. Soc., 4to, 2d series, vol. ii. plates 31, 32, 35.

2 Trans. Geol. Soc. Lond., 2d series, vol. iii. plate 13.

3 Memoirs of Wernerian Society, vol. vii. ; Trans. Highland Society, vols. xiii.
and xiv. ; Trans. Royal Society of Edinburgh, vol. xiv.

4 Sketch of the Geology of Fife and the Lothians, 1839 ; and various papers in
Trans. Roy. Soc. Edin., and Edin. Phil. Jour.

5 Trans. Highland Society, vol. xii.; Trans. Roy. Soc. Edin., vols. xiv. and xv,

6 Trans. High. Soc., vol. xiii. ; and Monograph on Dura Den, 1858.
' Mem. Wernerian Soc., vol. iii.

8 Trans. High. Soc., vol. xii.

9 Sketch of the Geology of Moray, 1842.

10 Mem. Wer. Soc., vol. ii. ; and various papers in Edin. Phil. Jour., and Trans.
Roy. Soc. Edin., &c.

11 Quar. Jour. Geol. Soc., vol. vii.; and the Geology and Palaeontology of the
British Isles, in Keith Johnston's Physical Atlas.

12 Edin. Phil. Journal, vol. xl. p. 76, and other papers.

13 Quarterly Journal Geological Society.

14 Trans. Roy. Soc. Edin., vol. xiii., "Description of Shetland Islands," 1822.

15 Mem. Wer. Soc., vols. i. and"ii. ; and Trans. Roy. Soc. Edin., vol. vi.

16 Trans. Highland Soc., vol. xii.
J7 Trans. Roy. Soc. Edin., vol. xiii.

knight,1 Menteath,2 Hugh Miller,3 Montgomery,4 Mcol,5 Page,6
Eamsay,7 Stevenson,8 Williams,9 Witham.10 Few of these
authors produced even local geological maps, but they made
such observations as were essential before any general map
could be begun.

Although Dr Macculloch collected many valuable materials,
and was indeed employed by government to lay the foundation
of a geological survey, he did not so embody his data as to
produce a general map in his lifetime ; and it was only after
his death, in the year 1832, that the Highland Society under-
took the task of having the data put together and published.
This map, though excellent as a beginning, was replete with
errors, and left very much to be desired as respected order and
classification.

Among the various authors who contributed valuable local
data, by which any generalising geologist might profit, Mr
Hay Cunningham produced a very creditable map of Suther-
land, and also contributed a map of the Lothians — both
accompanied by detailed descriptions.11 Mr Charles Maclaren,
in his excellent work, the Geology of Fife and the Lothians,
pointed out the distinctive characters of that grand lower
division of the carboniferous system around Edinburgh,
and threw much new light on the trappean rocks of that
district. In the southernmost counties, Mr D. Milne Home
brought out a map and description of Berwick and Koxburgh,

1 Mem. Wer. Soc., vols. ii. and iii.

2 Edin. Phil. Jour., vols. xviii. and xix.

3 The Old Red Sandstone, Footprints of the Creator, Testimony of the Rocks,
Cruise of the Betsy, Sketch-book of Popular Geology, and various papers in the
Witness newspaper.

4 Trans. High. Soc., vol. xii.

5 Trans. High. Soc., vols. xii. and xiv. ; Guide to the Geology of Scotland,
1844 ; Quar. Jour. Geol. Soc., various papers j Geological Map of Scotland, 1858 ;
Rep. Brit. Assoc., various papers.

6 Rep. Brit. Assoc. ; Text-books of Geology.

7 Geology of Arran, 1840.

8 Trans. Roy. Soc. Edin., and Quar. Jour. Geol. Soc.

9 History of the Mineral Kingdom.

10 Fossil Vegetables, 1831 ; Trans. Nat. Hist. Soc., Newcastle, vol. i.

11 See Trans, of Highland Society of Scotland, vols. xiii. and xiv.

B

6

and also completed an elaborate survey of the Mid-Lothian
Coal-field. In Dumfriesshire the basins of Eed Sandstone and
carboniferous rocks were separated from the underlying
" grauwacke " by Mr Menteath.

Although our illustrious countryman, Hugh Miller, did not
profess to produce geological maps, his writings have, in many
instances, led his contemporaries and followers to define the
relations of those strata of whose fossil contents he was so
admirable an expositor. Again, we should fail in expressing
the obligations we owe to various geologists of our country,
were we not to advert to the successive clear and instructive
works of Mr David Page ; whilst, in the sequel, it will be seen
that the labours of MM. Howell and Geikie of the Geological
Survey have been of essential importance.

As soon as the hilly countries of the south of Scotland,
hitherto classed under the unmeaning term of " Grauwacke,"
were shewn to contain fossils belonging to the great natural
series which I had named " Silurian," my interest in endeavour-
ing to bring the different rocks of my native countiy into cor-
relation with those of England and other lands naturally
augmented. With a view to the rectification of the errors of
Macculloch's map, and in the hope of establishing a more
correct classification, I induced Professor Nicol, who first
brought Scottish Silurian fossils into prominent notice,1 to
accompany me in a survey of parts of Ayr, Wigton, Galloway,
Dumfries, &c., during the summer of the year 1850 ; and the
result, accompanied with a map, was communicated by me to
the Geological Society,2 shewing the relations of various
Silurian deposits. '

A great desideratum, however, which I had long had at
heart, remained unaccomplished. An old observation of the
year 1827, in company with Professor Sedgwick, when we
noticed the superposition of the crystalline and micaceous
schists of Sutherland to the less altered quartz-rocks and lime-
stones of that tract, had for many years been present to my
mind, and had led me to hope that the day might come when,

1 Quar. Jour. Geol. Soc., vol. vi. p. 53. 2 Ibid., vol. vii. p. 137.

by the discovery of fossils in a portion of that series, coupled
with that clear order of superposition, the rocks of the High-
lands might be brought into concordance with well-known
palaeozoic formations in other parts of the world. The
discovery in 1854, by Mr Charles Peach, of certain organic
remains in the limestone of Durness, in Sutherland — combined
with the fact of the m/raposition of that rock, and its enclosing
quartzites, to vast masses of micaceous crystalline strata — at
once seemed to me to afford the fairest grounds for determining
the question ; and in order to work it out, I requested Professor
Mcol to be my companion, in the summer of 1855, in resur-
veying my old ground in the north-western Highlands.

The first result of these labours was in the same year laid
before the meeting of the British Association at Glasgow, when
Mr Nicol candidly stated his objections to some of my views ;
and afterwards (1856) revisiting the north-west of Scotland,
published his own opinions as to the order and equivalents of
the series.1 By referring to the memoirs we have written,2
the general reader who may compare the map of Mcol with
that which is now issued, will at once see that there are
essential and striking distinctions, both in the classification
and delineation of the rock-masses, between his ideas and
those of my colleague and myself.

Of such importance did the solution of the questions in
dispute seem to me, that I revisited the typical districts of the
north in 1859, accompanied by Professor Eamsay, and laid
the main results before the meeting of the British Association
at Aberdeen. In the following year I requested Mr Geikie
not only to look at some of those northern types, but also
to unite with me in shewing how they ranged into the
southern Highlands. Now, as both my associates of the Geo-
logical Survey have confirmed my views, and as the main data
have also been supported by the independent observations of
Colonel Sir Henry James and Professor Harkness, I had no
longer any hesitation in urging Mr Geikie to prepare this map,
being fully aware that in addition to all that had been done in

1 Quar. Jour. Geol. Soc., vol. xiii. p. 17.

3 In the Quarterly Journal of the Geological Society.

8

the north, his intimate acquaintance with the rocks of the south
of Scotland would render the work of essential service in
advancing Scottish geology.1

If, in the absence of correct topographical maps, a very long
time must elapse before any attempt can be made to publish a
geological map of Scotland on even a moderately large scale,
so as to offer details like those which are laid down in the
published Edinburgh sheet of the Geological Survey,2 enough
has already been done to enable my coadjutor and myself to
venture on the production of that which we consider to be a
requisite prelude to such future works, by placing the chief
rocks in their true sequence.

The map which we now issue has been prepared by Mr
Geikie. The Shetland and Orkney islands, with the counties
of Sutherland and Caithness (where their delineation differs
from that shewn on previous maps), are given as coloured
geologically by myself in my sketch-map of the north-west
Highlands,3 and the subdivisions of the Old Eed Sandstone of

1 In the year 1850 I satisfied myself that the chloritic schists and limestones,
as well as the micaceous schists, forming a great arch between the Firth of Clyde
and Loch Fyne, as well as the mica schists and limestones to the north of Inverary,
would prove to be of Silurian age (See Quar. Jour. Geol. Soc. Lond., vol. vii. p. 168,
and first edition of " Siluria," p. 163). During the autumn of the year 1860, the
area of my observation in that quarter was extended by Mr Jamieson of Ellon, in
Aberdeenshire, who has enabled us to define the south-western corner of the main-
land of Argyll and of the island of Rothesay by additional data respecting the
igneous rocks interpolated in the chloritic schists, on which subject he has
communicated his views to the Geological Society. I have also to state that, early
in the summer of 1860, Professor Harkness examined considerable tracts of country
between the southern Highland frontier, near Dunkeld, and the western coast, on
the Linnhe Loch, and arrived at the same conclusions as Mr Geikie and myself —
i. e., that the upper schistose series only, and occasionally based upon the upper
quartz -rock, is the dominant division in that southern region of the Highlands.

2 The joint work of Mr Howell and Mr Geikie. The memoir descriptive of this
sheet is now published.

3 By comparing the present map with my small sketch-map of the Highlands
(Quarterly Journal Geol. Soc., vol. xvi. p. 419*), it will be seen that the general
view expressed in the latter, that the crystalline rocks of the southern Highlands
would be found to be essentially repetitions of a portion of the stratified masses of
the north Highlands, has been sustained by the last survey of Mr Geikie and
myself ; whilst, through the zeal and ability of my colleague, the outlines, which
were simply suggestive, have now been rendered definite and clear.

the north generally are also inserted on my authority. The
main features of the Hebrides, with the marked distinction,
however, of the fundamental gneiss, remain as denned "by
Macculloch. Skye and Kaasay have indeed been resurveyed
by my colleague,1 who has introduced considerable changes in
those parts. The outlines of the islands of Islay and Jura,
along with the whole of the subdivisions of the metamorphic
series of the Highlands, from Sutherland to the Old Eed Sand-
stone barrier, were also mapped by him during our joint survey
last summer. The granitic tracts of the north-east, and part
of the igneous rocks of Argyllshire, are taken from Professor
Nicol's map ; and the greenstones of Cantyre from the paper of
Mr Jamieson referred to in a previous note.

The mapping of the greater part of the central region
between the metamorphic Silurian rocks of the north and their
less altered equivalents of the south, differing as it does so
essentially from all previous delineations, has been effected by
my colleague. The northern part of Haddingtonshire, however,
was surveyed (for the Geological Survey) by Professor Eamsay
and Mr Howell ; and the eastern part of Fife (also for the
Survey, but not yet published) is likewise the work of the
latter able geologist, who also mapped the details of the Mid-
Lothian coal-basin. The outlier of Permian and carboniferous
rocks at Closeburn, in Dumfriesshire, is taken from a tracing
sent us by Professor Harkness, to whom also are due any
changes that have been inserted in the relative boundaries of
these rocks in the valleys of the Nith and the Annan. The
island of Arran is from Professor Eamsay's map, except that
the New Eed Sandstone of former geologists is coloured by us
as carboniferous.

In the geological colouring of the Highlands, our work is
distinguished from all previous maps. We have as the base

1 We have coloured the islands of Tiree and Coll (which we did not visit) as
fundamental or Laurentian gneiss, on the suggestion of the Duke of Argyll, who
has recently assured me that the gneiss of which Tiree is composed is very distinct
from the so-called gneiss of the old maps in Argyllshire and the mainland. On
referring to Macculloch's description of the gneiss islands, I also find that Tiree
and Coll come under precisely the same description of hornblendic gneiss which
characterises Long Island and the outer Hebrides.

10

of the whole succession, in the island of Lewis, and the Outer
Hebrides, as well as along the north-western shores of the
mainland of Sutherland and Koss, a crystalline gneiss, which
occupies the same position as a similar rock in Canada,
described by Sir William Logan, and named by him the
" Laurentian System."1 This fundamental rock is marked on
our map by the Greek («) to denote its priority to the next
formation — the Cambrian — for which the Roman (a) has been
already adopted in the Geological Survey. Whilst the
Cambrian is the oldest known rock in England, Wales, and
Ireland, the Scottish fundamental gneiss is thus proved to be
the oldest rock in the British isles ; for it has no equivalent
in England, Wales, and Ireland. This Laurentian gneiss has
a prevalent N.W. S.E. strike, as is well shewn by the band of
limestone which it contains on the north-east shore of Loch
Maree, and which, it will be observed, is at right angles to the
strike of the superposed limestones of the neighbouring moun-
tainous tracts, and therefore wholly unconformable to them.
The Cambrian (a) consists, in the north-west of Scotland, of
brownish-red sandstones and conglomerates, resting in gently
inclined beds on the convoluted edges of the older gneiss. It
is admirably exhibited in the Applecross mountains, and also
along the wild shores of Loch Torridon, onwards to the head of
Loch Maree, as well as on the shores of Loch Broom, and in
Assynt, and on the west coast of Sutherland. On the truncated
edges of the Cambrian sandstones come the quartz-rock and
limestone (b' lx), which, in Sutherland and Ross, form the base
of the lower Silurian, as proved by their included fossils. The
limestone of Durness and Eriboll stretches southward by Loch
Assynt to Loch Broom, and is seen at intervals onwards to the
south end of Skye, where, as shewn on the map, a small outlier
occurs on the margin of Loch Eishort. Through the whole of
this long course it everywhere rests with its associated quartz-
rocks unconformably on the Cambrian.

The wild tract of country from the west coast to the line of
the Caledonian Canal may be regarded as a great synclinal

1 Quar. Jotir. Geol. Soc., May 1861. Section!., at the top of the present Map,
exhibits the whole succession of rock-masses in the north of Scotland.

11

trough ; for the quartz-rocks and limestones which form its
western boundary rise up again on its eastern side, and are
seen along the chain of lochs that stretches from Inverness to
Oban, whence they are continued in the islands of Garveloch,
Scarba, Jura, and Islay. This remarkable line of lakes is,
therefore, an anticlinal axis, broken through by a coincident
line of fissure. From this line the limestones and quartz-rocks
roll over to the eastward, but their upper portions rise again
and again to the surface in a series of broad undulations, as
has been attempted to be shewn on the map, and in the long
section, No. 2. Above this group comes a perfectly conformable
series of quartzose, gneissose, and schistose rocks (b' 1), which
form the great mass of the mountains from the north coast of
Sutherland to the Highland border. The thickness of this
series must be very great ; but, at the same time, the endless
plications of its component strata must increase enormously
its apparent extent. The section, No. 2, is meant to exhibit a
generalised view of the succession of this upper metamorphic
group, which is clearly the equivalent of the greywacke, sand-
stone, and shale, that form the lower silurian tracts (b 1) of
the south of Scotland

The lower Silurian formation of the south of Scotland is
likewise thrown into very numerous anticlinal and synclinal
axes ; but it may be regarded, on the whole, as bent into a
great arch, the centre of which runs from south-west to north-
east, passing to the south of the town of Moffat. South of
this line the strata dip, on the whole, towards the south-east,
and, in the headlands of Kirkcudbright, as in the Cumberland
mountains, are succeeded by upper Silurian strata. On the
north side of the anticlinal line they dip north-west until they
are flanked unconformably by the Old Eed Sandstone and Car-
boniferous formations. But that the upper Silurian exists also
on this side of the arch, is shewn by the two isolated patches
of Lesmahagow and the Pentland Hills, which are abundantly
fossiliferous, and are in both localities overlaid unconformably
by upper Old Ked or Carboniferous sandstones.

The triple division of the Old Eed Sandstone, which exists
in the north of Scotland, is clearly indicated, even on the small

12

scale of the present map. In the south, as shewn by Mr
Geikie's recent researches, there is a great hiatus below the
upper member of the formation, which shades up into the
Carboniferous, and rests quite unconformably on the lower
Old Red Sandstone, the middle portion not having been as yet
satisfactorily established to the south of the Grampians. The
igneous rocks,1 associated with the Old Eed Sandstone of
Scotland, are of two kinds — first, felspathic rocks, as felstones,
porphyries, amygdaloids, and interstratifications of submarine
volcanic ejections or ashes, all contemporaneous with the strata
among which they occur. Of this group, the Sidlaw, Ochil,
and Pentland Hills may be taken as examples, as well as much
of the igneous rock between the Campsie Hills and the south
of Ayrshire. The second kind of Old Red igneous rocks are
extensive masses of greenstone, basalt, and various felstones ;
which, however, have possibly no chronological union with
the rocks which they traverse. The greenstones are well seen
in some of the larger craggy hills near Jedburgh, at Dunse,
and at different localities along the great central basin of the
country. The felstones are abundant in the uplands of
Lanarkshire, Tinto, and many of the neighbouring hills of
this group.

Another chief feature of the present map, as distinguished
from all previous maps of the country, exists in the sub-
division of the Carboniferous formation. This group of rocks
consists, in Scotland, of the following members :

English equivalents.

Upper or ' ' Flat " coals, . . = Coal-measures.

"Moor-rock" or Roslyn sandstones, = Millstone grit and upper limestone shales.
Lower or « Edge " coals, . = Carboniferous ilmestone.

Carboniferous limestones, . )
Calciferous sandstones, . = Lower limestone shales.

The upper coals represent, in whole or part, the true English

1 A close scrutiny of the igneous rocks has enabled my colleague to establish cer-
tain marked distinctions between those which were formed contemporaneously with
the sedimentary deposits, and those which have been subsequently erupted. The
distinction is shewn on the map by two tints of crimson — the darker shade marking
the intruded masses, while the lighter represents those of contemporaneous origin.

13

coal-measures which lie above the millstone grit. They occur,
in Scotland, in four basins — one in Mid-Lothian, a second in
Fife, the third along the Clyde, south-east of Glasgow and
eastwards to Bathgate, while the fourth occupies a large area
of Ayrshire. The position of the millstone grit in Scotland,
although known, has not yet been satisfactorily traced, and is
therefore not shewn on the present map. The lower coals are
interstratified in their higher and lower portions with seams
of marine limestone, the fossils of which identify the series as
the equivalent, partly terrestrial, partly marine, of the Car-
boniferous limestones of England. This series is coloured on
our map with one tint, it being found impossible, on so small
a scale, to insert the lines of limestone. The Calciferous
sandstone group consists of a great series of sandstones, shales,
and thin limestones of a mingled marine, estuarine, or fluvia-
tile character, containing plants, as stigmarise, sigillariae,
calamites, ferns, conifers, &c. It occurs in its greatest
development in the eastern part of the great central basin
of the country, and thins out rapidly to the south-west, so
that in Lanarkshire and Ayrshire it is in many places
wholly wanting, and the Carboniferous limestones rest
directly on the felstones and sandstones of the Old Eed
group.1

The igneous rocks associated with the Carboniferous forma-
tion in Scotland are both contemporaneous and intrusive. Of
the former kind (greenstones, basalts, felstones, and ashes or
tuffs), the area of the Lothians, especially Arthur's Seat at
Edinburgh, the Garlton Hills of Haddingtonshire, and the
Bathgate Hills of Linlithgowshire, afford characteristic ex-
amples. To the intrusive igneous rocks (chiefly greenstones
and basalts, more rarely felstones) belong the craggy hills
throughout the centre of the country, as Stirling Eock, Binny
Craig, Castle Eock of Edinburgh, and many others.

To the Permian formation (e) we refer provisionally those
red sandstones of Dumfriesshire in which the footsteps of
tortoises occur at Corncockle Moor ; but on this point we also

1 See Mr Geikie's paper, Quar. Jour. Geol. Soc., vol. xvi. p. 312 et seq.

14

think that some of the red rocks of that tract must certainly
be grouped with carboniferous strata.

Of the small patches which are as yet uncertainly referred
to the trias (f), we can say little or nothing until their
relations be more accurately determined.

As to the lias and oolitic deposits of the north, to which
some of my earliest labours were devoted,1 I may say that,
owing to the researches of the late Professor Edward Forbes
and of my associate, their relations in the Hebrides, particu-
larly in Skye and the adjacent isles, have been much more
clearly eliminated.2

No attempt is made in this map to represent the small
patches of the older tertiary rocks, which have as yet been
recognised so very partially in Scotland ; and still less is it
practicable to define, on such a small scale, each tract which is
covered by various superficial detritus, whether the ancient
boulder or glacial drift, or the so-called " Till " of certain
great estuaries. Our sole object is to give a view of the chief
palaeozoic and mesozoic deposits, together with the igneous
rocks, of which the framework of Scotland is mainly com-
posed, by classifying these according to their age — and to
correlate such portions of them as have been subjected to
metamorphism, with others in which the original sediment
has been much less altered.

To make the present map as far as possible self-explana-
tory, my colleague has inserted along the margin several
transverse sections, through different parts of the country, to
shew the general succession of the rock-masses.

SECTION I. — Generalised Section of the Crystalline Rocks of the
Northern Highlands,

at the head of the map, is enlarged from one in my memoirs
on the Northern Highlands, and represents, in a generalised
form, the order of superposition of the various sedimentary

1 Trans. Geol. Soc., 2d series, 4to, vol. ii. p. 353.

2 Quar. Jour. Geol. Soc., vols. vii. and xiv. p. 1.

15

deposits from the Hebrides across Sutherland to Brora. On
the west coast, the fundamental gneiss •(«) is shewn to be
unconformably overlaid by the Cambrian sandstones (a) ;
these, again, also unconformably by the lower Silurian quartz-
rocks and limestones, with fossils (b' 1*), which pass upward
in regular succession into the crystalline schists (b' 1), that
spread out in huge folds over the greater part of Sutherland,
until their broken edges, much intermingled with granite, are
covered by the Old Bed Sandstone (c), which is formed out of
their debris, and is itself unconformably overlaid by the lias
and oolite (g) of Helmsdale, Brora, and Golspie, which I
formerly described.1

SECTION II. — From Dunvegan Head, SJcye, across Scotland to
the Cheviot Hills,

is drawn along a line transverse to the strike of the country,
and gives the best typical section of the rocks. The north-
west end, as unravelled and described by Mr Geikie, begins
at Dunvegan Head, Skye, among sheets of greenstone, which
contain interstratified seams of estuary limestone, shale, and
coal — all belonging to the middle Oolite. These stretch
towards the south-east, until they are broken through by some
enormous mountain-masses of syenite, which, at Loch Sli-
gachan, have brought up a portion of the Cambrian sandstone
that forms the pavement of the secondary rocks in this part
of the country. Beyond the syenite lies the valley of Strath,
occupied by Lias limestones and shales — the greatest breadth
of that formation in Scotland. The Cambrian sandstones
appear along an anticlinal ridge in the middle of the Strath,
and come up again on the south side, from below the second-
ary rocks.2 The ground here is much faulted, but eventually,
on the south-east side, we get the limestone and quartz-rock
of the lower Silurian series, forming, with their overlying
schists, almost the whole of the peninsula of Sleat. Here

1 Trans. Geol. Soc. Lond., 4to, 2d Series, vol. ii. p. 253, with map.

2 See Mr Geikie's paper, Quar. Jour. Geol. Soc., vol. xiv. p. 1 et seq.

16

these strata have a south-east dip ; so that, after crossing the
narrow strait which intervenes between Skye and the main-
land, we come to higher members of the same lower Silurian
series, in the form of quartzose flagstones, graduating upward
into schists with limestones. The schistose series, which now
supervenes, is probably repeated upon itself in endless plica-
tions.1 On the whole, however, the dip is south-easterly
along this section, as far as a line drawn from the middle of
Loch Quoich to the watershed between Kinloch-Aylort and
Prince Charles's Monument. This line is a synclinal axis,
and on its eastern side the same schistose series is repeated,
with a prevailing north-westerly dip, until, about the head of
Loch Eil, the quartzose flagstones are brought up again.
These undulate to the line of the Caledonian Canal, and then
dip again to the south-east, so that the schistose series
reappears above them. The remarkable chain of Lochs from
Inverness to Inverlochy has been already referred to as an
anticlinal axis, broken through by a coincident line of fault.
The folding of the arch is clearly shewn in the section. That
part of the line which crosses Ben Nevis has been inserted
from an examination of the two transverse sections to the
north and south of that mountain — the one up Glen Spean,
the other along the shores of Loch Leven. The schists and
limestones undulate towards the Moor of Eannoch, where the
subjacent quartzose flaggy beds reach the surface, arching
among broken irregular masses of granite and porphyry. The
whole of this region is pre-eminently mineralised. At Glen
Lyon, however, the south-east dip returns, and the flagstones
plunge below the schists and limestones. Ben Lawers, like
Ben Nevis, stands in the centre of a synclinal trough — a
monument of enormous denudation. The limestones of Glen
Lyon, which sink below it on the north-west side, rise from
under it on the south-east, and are well seen along the banks
of Loch Tay. That valley lies on an anticlinal fold, so that
the limestones bend over, and on the other bank dip away to
the south-east, undulating with their superjacent schists,

1 This is more fully shewn in our joint Memoir on the Highlands ; Quar. Jour.
Geol. Soc. for May 1861, p. 171 et seq.

17

until the whole is unconformably overlaid by the conglo-
merates of the Old Eed Sandstone. The broad undulating
country between the Highland border and the Ochil Hills is
occupied by Old Eed Sandstone. The relation of the fel-
spathic rocks of these hills to the latter formation has not yet
been adequately ascertained. My colleague believes that, in
some part of the district, an unconformity will be found, and
that the upper part of the series, graduating upward into the
sandstones of Dura Den, will be seen to overlap the older or
Arbroath flagstones. It remains yet to be discovered whether
or not the felspathic rocks of the Ochils are of two ages, one
series lying on the edges of the other. Altogether, this part
of the section must still be held as doubtful ground. The
Carboniferous rocks in the Devon valley, according to recent
and unpublished observations of my colleague, seem to over-
lap the Ochil felstones. Here Mr Geikie finds the whole of
the lower Carboniferous sandstones and shales (so enormous
a depth of strata in the Lothians and the east of Fife) to be
almost wholly wanting — the Carboniferous limestones forming
nearly the base of the series at the point where the present
line of section crosses. From this locality he has traced
them dipping under the volcanic ash of the Saline Hills, and
rising again on the south-east, where once more they sink
below the lower group of coals which form the Dunfermline
coal-field. The section now crosses the Forth, and shews, on
the south side, some of the under portions of the great lower
Carboniferous series, which was absent on the north side.
Arthur's Seat occurs in this low part of the group, and is
explained in a separate section (No. 4). It will be seen that
the north-west side of the Mid-Lothian coal-basin is bounded
by a line of powerful fissure, which flanks the south-eastern
side of the Pentland Hills. The details of this coal-field
have been completely elucidated by Mr Howell on the
Edinburgh sheet of the Geological Survey, to which, and to
its accompanying Memoir, now published, the reader must
refer for fuller information. It is enough to remark here,
that the anticlinal arch of Eoman Camp Hill, consisting of
the lower limestones, has thrown this great expanse of Car-

18

boniferous strata into two troughs, known as the basins of
Edinburgh and Haddington (or Mid-Lothian and East
Lothian). The great Silurian region of the south of Scotland
becomes much attenuated towards the north-east, owing to
the encroachment of later deposits. Where crossed by the
present line of section, it consists of greywacke grits, sand-
stones, and shales, much hardened, and thrown into highly-
inclined convoluted foldings. The prevailing dip, however,
trends towards the north-west, below the central basin of the
country, from under which the same strata (according to our
belief) reappear on the north-west side, as the highly-meta-
morphosed schistose or gneissose rocks of the Highlands,
already described. A cake of Old Eed conglomerate lies in
the hollow along the watershed near Soutra Hill ; and similar
deposits occupy the valley of the Leader (down which the
line of section runs), and most of the intervening ground to
the foot of the Cheviot Hills. Much has still to be done in
disentangling the details of the igneous masses in this region.
Some are older than the Old Eed, others later; wThile some
may possibly be contemporaneous with parts of that forma-
tion. The Cheviot Hills consist of an enormous succession of
various felspathic masses, which were erupted previous to the
deposition of the adjacent Old Eed Sandstone and lower Car-
boniferous rocks, as was clearly shewn many years ago by
Mr Milne Home.1 As, however, all the Old Eed Sandstone
of this locality belongs to the upper part of that formation, it
is quite possible that the Cheviot porphyries were thrown
out during the deposition elsewhere of the middle Old Eed
Sandstone, as was probably the case with the porphyries of
Lanarkshire.

SECTION III. — From Ben Lomond to the Cheviot Hills.

Ben Lomond consists of the crystalline schists described in
the previous sections, which here shew in some places pebble-

1 Trans. Eoy. Soc. Edin., vol. xiv. p. 253 (1836).

19

beds, clearly proving their original aqueous origin. The Old
Bed Sandstone and conglomerate rest unconformably upon
these schists as in all other parts of the country. We infer
that these strata belong here to the base of the formation, and
are therefore a prolongation of the Forfarshire series. But
on approaching the north-west flanks of the Campsie Hills,
we find a series of sandstones, and marls, and thin limestones,
the position of which is not yet adequately fixed.1 They are
known to Glasgow geologists by the name of the " Ballagan
Beds," and, according to Mr John Young, of the College
Museum, Glasgow, contain a few plants (lepidodendra and
catamites). Mr Geikie compares them with a very similar
series of deposits which, in Berwickshire, form the lower
Carboniferous group ; but he suggests that, as that group seems
everywhere thinning out to the west, the Ballagan beds may
rather be a prolongation of the red and green sandstones and
marls (Upper Old Eed Sandstone), which range from Dura Den
along the north flank of the Lomond and Cleish Hills toward
the plain of Stirling, and may reappear again in the Campsie
range. If this be the case, he suggests further that a careful
search should be instituted to note whether the limestone
of Campsie can be traced transgressively over the Ballagan
beds, and whether these latter lie unconformably on the Old
Eed Sandstones that range up towards the Highland Border.
The igneous rocks of the Campsie Hills (felstones, greenstones,
&c.) occur in great parallel sheets between the strata ; but it has
not been sufficiently determined whether they are truly con-
temporaneous ejections, though it seems most probable that
they are. The Campsie limestones have been well described
in Mr Young's paper quoted in a previous note. With their
overlying coals forming, as a whole, the equivalent of the
" edge " or lower coals of Mid-Lothian, Fife, and Linlithgow
(= the Carboniferous limestone series of English geologists),
they dip below the upper coals (=the English Coal-measures)
that form the Clyde basin, and stretch east to Bathgate. At

1 See Dr Bryce's volume on the Geology of Clydesdale, 1859 ; and a good
palaeontological paper by Mr Young, recently published by the Geological Society
of Glasgow.

20

the latter locality the lower coals again emerge, along with
their accompanying limestones. Here they are associated
with one of the most interesting and complicated assemblages
of contemporaneous and intruded igneous rocks to be found
in Scotland.1 From the Bathgate Hills the lower Carboniferous
group (= the lower Limestone Shales of England and Ireland)
occupies the whole district up to the summit of the Cairn
Hills, at the south-west end of the Pentland range. This
group consists chiefly of sandstones and shales ; but there are
also many seams of limestone, and one of coal Of the lime-
stones the most important is that which (from having been
first studied at Burdie House, four miles south of Edinburgh2)
has been termed the Burdie House limestone. It contains the
remains of terrestrial plants, cyprides, and fishes — pointing to
ancient estuarine conditions of deposit. The coal-seam of
the lower Carboniferous group of Linlithgowshire is known
as the Houston coal, but is very inconstant, and does not occur
in Edinburghshire.3 The whole lower Carboniferous series
indicates the former existence of a wide estuary or series of
brackish-water lagoons over the eastern part of central
Scotland — a condition of things which was terminated by a
subsidence below the sea which gave rise to the formation of
the lower and purely marine part of the Carboniferous lime-
stones, although terrestrial surfaces reappeared before these
limestones had accumulated more than a few feet. From that
period the area remained sometimes terrestrial, frequently
subaqueous. After the deposition of the upper limestones,
such calcareous beds ceased to be formed, although the alter-
nations of sandstone, shale, fire-clay, and coal, sufficiently
prove how completely the terrestrial surfaces were submerged
and covered by accumulations of sediment. The Cairn Hills
consist of the lower parts of the Carboniferous formation gradu-
ating downward into the upper Old Eed Sandstone, which, as

1 This district has been unravelled by Mr Geikie, and his detailed description
will be found in the Memoir to accompany Sheet 32 of the Geological Survey of
Scotland.

2 See Dr Hibbert's Paper, Trans. Roy. Soc. Edin., vol. xiii. p. 169.

3 For further details, see Mr Geikie's Memoir just referred to.

21

shewn in the section, rests unconfonnably on the lower Old Bed
Sandstone and the upper Silurian shales and grits of the Pent-
land Hills. These Silurian rocks have been ascertained by
Mr Geikie to be abundantly fossiliferous.1 A fault on the
south-east flank of the Pentland Hills, as shewn in the section,
has thrown down the Carboniferous strata against the Old Ked
conglomerates. The section crosses here about the village of
Carlops, where, in the bed of the river Esk, some instructive
sections are visible. These Carboniferous rocks belong to
the Carboniferous limestone series, and form a small basin,
which is a prolongation of that of Mid-Lothian. Along the
edge of this basin, south-east from Carlops, the limestones,
with their associated strata, rest quite unconformably on the
highly inclined lower Silurian shales and grits, and thus a
great part of the lower Carboniferous series is here wanting.
The Silurian Eocks seen in this part of the section belong to
the same region traversed by the southern part of Section II.
The upper Old Eed Sandstone of the Teviot valley also corre-
sponds to that of the Leader and Tweed, and the Cheviot Hills
require no further description.

SECTION IV. — Detailed Section of Arthur's Seat, Edinburgh.

This Section explains the structure of Arthur's Seat as
worked out by Mr Geikie during the progress of the Geological
Survey in Scotland. It will be seen from the section that the
hill is formed of two portions — one consisting of inclined
sandstones, shales, greenstones, and ash-beds of lower Car-
boniferous age covered unconformably by the other, which
is made up of various volcanic ejections. The lower and older
series of igneous products shews that during the lower Carbon-
iferous period a volcanic orifice existed at Edinburgh, which
emitted showers of ash and streams of molten matter. After
this vent had been dormant, apparently for a vast geological
cycle, during which the rest of the Carboniferous formation

1 For lists of fossils, and a description of the physical geology of these hills, see
his Memoir.

22

had been deposited, and Scotland had assumed very much its
present appearance, the volcanic forces broke forth again, and
ejected the later mass of coarse conglomerate and basalt which
covers over the denuded edges of the older series. The crater
from which these materials issued was eventually closed by a
column of basalt that rose up, and gradually hardened. Its
denuded top forms now the summit of the hill. For complete
details of this hill, and of the surrounding region generally,
the reader must consult the Memoir descriptive of Sheet 32
of the Geological Survey of Scotland, and also the faithful
description of Mr Maclaren in his Sketch of the Geology of Fife
and the Lothians.

In offering this outline to the public, we are well aware that
the day is yet distant when the exact boundary-lines of for-
mations, and the position of all the dislocations of the crust
can be inserted ; and hence we have chosen a sheet of such
small dimensions only as will convey our general views as
to the relative antiquity of the chief rock-masses.

Those who wish to make themselves more fully acquainted
with the grounds on which this map is constructed, must
consult the Memoirs and numerous sections we have already
published in the Quarterly Journal of the Geological Society ;
as well as the various works by other geologists, quoted on a
preceding page.1

1 See Murchison, Siluria, p. 137 ; Quar. Jour. Geol. Soc., vol. xii. p. 15 ; vol.xiv.
p. 531 ; vol. xv. p. 353 ; ib. 419 ; vol. xvi. p. 215. Lecture before the Aberdeen
Meeting of the British Association, 1859. Geikie, ib. vol. xvi. p. 1 ; and vol. xvi.
p. 312. Rep. Brit. Association for 1859, p. 106. Proc. Roy. Soc. Edin., iv. 309
and 453. Trans. Roy. Soc. Edin., vol. xxii. p. 633. Memoirs of Geological Survey
(description of Sheet 32, Scotland). Story of a Boulder, 1858, p. 178 et seq. As
bearing on the question of the metamorphism of the Scottish Highlands, reference
should also be made here to the labours of foreign mineralogists ; especially to the
analyses of Berthier, Mitcherlich, &c., on simple minerals ; Delesse on the metamor-
phism of rocks ; and Dobree's "Experiences Synthetiques, " &c., Paris, 1859. See
also Mr Sterry Hunt's papers in the Memoirs of the Geological Survey of Canada ;
as well as those of Mr Sorby, Professor Tyndall, and others in our own country.

23

In conclusion, let me say that, in publishing this general
Geological Map of Scotland, Mr Keith Johnston, who has
constructed the topography with his well-known ability, has
also inserted the heights of the principal mountains, and that
my colleague and self have added the names of certain places
which are of geological importance.

RODERICK I. MURCHISOK

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